Scavenging and supply of combustion air to two-cycle engines



1936- I E. B. POLLISTER' 2,062,821

SCAVENGING AND SUPPLY OF COMBUSTION AIR TO TWO-CYCLE ENGINES Filed Sept.4, 1931 INVENTOR. MIRD B.POLL1S7R By /W /,zz

LA TTORNEYS.

Patented Dec. 1, 1936 UNITED STATES PATENT OFFICE SCAVENGING AND SUPPLYOF COMBUS- TION AIR TO TWO-CYCLE ENGINES Application September 4, 1931,Serial No. 561,130

9 Claims.

The object of the invention is the improvement in general efi'iciency oftwo-cycle internal-combustion engines, more particularly high speed,injection type engines, through improved scavenging accomplished by theuse of air from different pretssure sources, as hereinbelow more fullyset or h.

In engines of. the type to which this invention particularly relates andwhich have exhaust and scavenging ports uncovered by the piston andwhich use scavening air at the usual scavenging pressure, and whether ornot such air also serves for super-charging, the scavenging is apt to beeither imperfect or else wasteful of air, because of the shortness ofthe time available, and where such cylinders have also been served withair of higher pressure, for super-charging, the manner of introductionof the air for this purpose has not been such as appreciably toaccelerate the scavenging nor be efficient for the scavenging purpose.According to my invention a limited injection of. air at an adequatelyhigh pressure is made to supplement a larger volume of air from a lowerpressure source in such way as to clear the combustion space andparticularly the upper part or clearance end thereof with unusualrapidity so that efiective scavenging is accomplished in spite of thehigh speed and large piston displacement and without excessive powercost for this work. This is accomplished by the provision of a source ofair of considerably higher pressure than ordinarily used for scavenging,and of special scavenging ports for such high pressure air which areuncovered by the piston on its out or down stroke and which are disposedat an acute angle, pointing upward or toward the clearance space, theaction of such ports being appropriately timed so that one or more highvelocity jets issue therefrom coincidently with or during the flow ofthe normal or low pressure scavenging air, stimulating the movement ofthe latter, and at the same time, because of their acute angle, drivingthe combustion products from the upper part of the cylinder downwardstoward the exhaust ports, the effect being generally equivalent to theuse of a larger air volume from a single source of scavenging air at apressure higher than that of the low-pressure air in this invention; butwithout the attendant expense incident to such larger quantity andhigher pressure. Within the scope of the invention the same highpressure means can also be used for supercharging the engine when or ifdesired, as by appropriately designing the air admission timing.

Fig. 1 of the drawing is a more or less diagrammatic section of. anengine cylinder embodying one of the possible forms of the invention, at

present preferred, and Fig. 2 is a section on the line II-II of Fig. 1,showing also, in diagram, the air sup-ply sources for the high and lowpressure ducts.

The engine cylinder I has exhaust discharge means in the form of a tierof ports 2 uncovered on the downstroke of the piston 3 and on theopposite side a series of admission ports for scavenging air, alsouncovered by the piston, the engine being assumed to be of, the fuelinjection type. As illustrated the normal scavenging ports are arrangedin two tiers although this is by no means indispensable. The lower tier4 is located to be uncovered by the piston after the exhaust port isopen on the downward stroke, and the upper tier 5 is uncovered beforethe exhaust is opened and these ports are preferably controlledautomatically, as by the pivoted louvers 6 or light and easily movedhorizontally-pivoted vanes opening toward the cylinder whenever thepressure therein is less than that of the air on the outside of thelouvers. Both tiers are supplied with scavenging air by a duct orreceiver 1 which is connected with an appropriate source 8 of lowpressure air, at say a pressure of one to three pounds above atmosphere.7

A separate source 9, of air at a higher pressure say about six to eightpounds above atmosphere, supplies a duct or receiver l0 having a port ortier of ports H discharging into the cylinder in proximity to the lowerpressure ports 6 and 5. The location of this discharge is subject tovariation to suit conditions in hand, and, likewise, it may becontrolled in any usual appropriate manner, as by the piston, or bytimed or automatic valves. In the preferred embodiment however, theports II are located in the opposite half of the cylinder from theexhaust port or ports 2 and above but adjacent the upper tier ofscavenging ports 5, and formed at an angle with the cylinder axis moreacute than that of the less inclined ports 5, so as to discharge towardthe upper end of the cylinder, and their aggregate cross area-ismaterially less than that of the low pressure ports. For example, withhigh-pressure air at a pressure of between six and eight pounds theaggregate area of the high-pressure ports is usually about eight percentof that of the other ports. An automatic valve l2 (which may be like oneof the louvers 6 previously described), opening toward the cylinder,when the pressure therein permits, is

illustrated as the means for controlling the high pressure air flow fromduct l0, and when thus controlled the high pressure air ports dischargewhenever their air supply pressure exceeds that within the cylinder, andsome of the high pressure air in this case serves for super-charging.But while the exhaust port is open these jets serve for scavenging onlyand their efiicient action is the result not of their volume but oftheir velocity, and the fact that their path due to the velocity enablesthe air to reach and sweep the upper end of the cylinder, and to directand stimulate the flow of the part of the air from ports 5 in a similarpath. Accordingly, the amount of such higher-pressure air need be butsmall and, in any event, the power cost of producing it is more thancompensated by the increased speed and thoroughness of the scavengingaction, which results in increased capacity and better efficiency of theengine.

Although so illustrated, the invention is not limited to application toa single cylinder or any particular type of two-cycle engine and theducts I and may therefore be understood as supplying high and lowpressure air respectively to as many cylinders as may be desired.

Reference is made to Patent No. 1,978,816, October 30, 1934, issued on aco-pending application of mine.

It will be understood that my invention is not limited to the details ofconstruction and operation described above and illustrated in thedrawing except as appears hereinafter in the claims.

I claim:

1. The method of scavenging a two-cycle engine cylinder having overrunexhaust and scavenging ports which consists in coincidently directinglow pressure air across the lower part of the cylinder and a smallervolume of air at higher pressure and velocity upwardly into the upperpart of said cylinder, bothwhile the exhaust port is open and both fromsubstantially the same part of the entrance side of the cylinder.

2. The method of scavenging a two-cycle engine cylinder having overrunexhaust and scavenging ports which consists in directing low pressureair into the lower part thereof and, simultaneously, a relatively smallvolume of air at high velocity upwardly toward the upper end of thecylinder, the point of entrance of the high velocity air into thecylinder being substantially above the entrance of the low pressure air.

3. The method of scavenging a two-cycle engine cylinder having overrunexhaust and scavenging ports which consists in coincidently directinglow pressure air across the lower part of the cylinder and a smallervolume of air at higher pressure and velocity upwardly into the upperpart of said cylinder, both while the exhaust port is open and both fromthe side of the cylinder opposite the exhaust port or ports.

4. scavenging means for a two-cycle engine cylinder comprising incombination with an exhaust port open when the piston is near the end ofits outward stroke, one or more scavenging air ports uncovered by thepiston in that position, one or more supplemental and upwardly directedair admission ports of less aggregate cross area, both said scavengingand supplemental air admission ports being at the opposite side of thecylinder from said exhaust port, and means to supply low and highpressure air for scavenging to said scavenging and supplemental portsrespectively, the said high pressure air means supplying air throughsaid supplemental port or ports during the discharge of air through saidscavenging air port or ports.

5. scavenging means for a two-cycle engine cylinder comprising incombination with an exhaust port open when the piston is near the end ofits outward stroke, a tier of scavenging air ports uncovered by thepiston in that position, one or more supplemental and upwardly directedair admission ports of less aggregate cross area, sources of low andhigh pressure air connected respectively to said scavenging andsupplemental ports and means for admitting the higher pressure airthrough said supplemental port or ports during the discharge of airthrough the other ports.

6. In a two-cycle internal combustion engine the combination of anexhaust port, an air admission port located to be uncovered by thepiston after the exhaust port is opened and a source of supply of lowpressure air connected to said admission port, a restricted airadmission port, a source of higher pressure air, a duct connecting thesame with said restricted port, the latter arranged at an angle so acuteas to direct the high pressure air discharge towards the top of thecylinder and means for admitting the higher pressure air through saidrestricted port during the discharge of air through the first mentionedair port.

7. In a two-cycle internal combustion engine, the combination of anexhaust port, an air admission port located to be uncovered by thepiston after the exhaust port is opened, a source of supply of lowpressure air connected to said admission port, a second air admissionport, located above the piston when the same is covering the exhaustport and in substantially the same angular position in the cylinder wallas the first mentioned air admission port, and a second source of airsupply, of higher pressure, connected to said second port to supplyscavenging air therethrough during the flow of low pressure air throughthe first mentioned air admission port, the second mentioned airadmission port being of restricted cross-section so as to discharge arelatively small volume of air and so formed as to discharge the sametowards the upper part of the cylinder.

8. In a two-cycle internal combustion engine, the combination of asource of low pressure air, a source of higher pressure air, a ductreceiving air from the first of said sources and a duct receiving airfrom the second of said sources; a cylinder, a piston working thereinand exhaust gas discharge means; a plurality of ports in the wall of thecylinder constituting outlets from the low pressure air duct and aplurality of ports in the cylinder wall constituting outlets from thehigh pressure air duct and discharging into the cylinder while said lowpressure ports are discharging into the cylinder, the said high pressureports being arranged to discharge into the cylinder above the pistonwhen the latter is in the position, on its inward stroke, at which theoutflow of exhaust gases ceases, and said low pressure ports beingdisposed to discharge their air toward the upper part of the cylinderand said high pressure ports being adapted to discharge their air at anangle with the cylinder axis more acute than that at which the lowpressure ports discharge.

9. In a two-cycle internal combustion engine, the combination of anengine cylinder having an exhaust port in a side wall thereof to becovered and uncovered by the piston, an air admission port located to beuncovered by the piston before said exhaust port is opened, means tosupply scavenging air to said air admission port, a second air admissionport also located to be uncovered by the piston as the piston approachesthe end of its combustion stroke, said second air admission port beingarranged at an acute angle so as to direct the air entering therethroughto-

